By Dan De LuceDan De Luce is Foreign Policy’s chief national security correspondent. He joined FP in June 2015 after working as Pentagon correspondent for Agence France-Presse. Prior to that, Dan reported for the Guardian from Iran until he was expelled by the regime in 2004. After the end of communist rule in Eastern Europe, Dan worked as a freelance journalist in Prague. He later covered the war in former Yugoslavia for Reuters from 1993 to 1995 before serving as Sarajevo bureau chief after the conflict. Born and raised in Los Angeles, Dan lives in Washington with his wife, journalist and author Caitriona Palmer, and his four children.

China would risk a potential military confrontation with the United States if it started dredging on a disputed shoal off the coast of the Philippines, retired U.S. Navy Adm. Dennis Blair said Thursday. And in a clash with the United States and its allies in the Philippines, Beijing almost certainly would lose, he said.

“If the Chinese push there, I think there’s going to be trouble,” said Blair, who once oversaw U.S. forces in the region as the former four-star head of Pacific Command. “And it’s trouble that the United States and the Philippines are going to win because the military situation is set up that way.”

To assert its power in the South China Sea and back up its expansionist territorial claims, Beijing has sent out fishing fleets in contested waters and built up artificial islands atop reefs in the past two year years, constructing airstrips and deep-water harbors that can accommodate naval ships.

In a growing rivalry over the strategic waterway, both China and the United States have stepped up patrols of naval ships, reconnaissance planes, and fighter jets in the disputed waters. The deployments have amounted to “shadow boxing” between the two powers and the risk of conflict has remained relatively low, said Blair, who also served as director of national intelligence during President Barack Obama’s first term.

But unlike the disputed Spratly Islands, which are the subject of multiple rival claims from China and several other Southeast Asian countries, the Scarborough Shoal effectively pits Beijing directly against Manila.

With the shoal located less than 150 miles from the Philippines, but 500 miles from China, experts believe Manila has a strong legal case in the disputed claims. The stakes are high as the Philippines has a mutual defense treaty with the United States that could possibly be invoked if Manila sought to defend what it considers sovereign territory.

“I would be surprised if the United States hasn’t told China it’s a shoal too far for them,” Blair told a group of reporters at a briefing at the Sasakawa Peace Foundation, where he serves as CEO. “It hasn’t been said publicly, but I hope we have done so privately.”

Tensions rose this week at the shoal after Chinese Coast Guard vessels prevented a Philippine nationalist group from planting a Filipino flag on one of the rock outcroppings.

The shoal is one of many maritime disputes at the center of a legal case the Philippines has brought against China before an international court in The Hague. The Permanent Court of Arbitration is due to rule this month on the case, but China has already vowed to ignore the tribunal’s decision, which is expected to favor Manila.

If China succeeded in taking over Scarborough, it could build airstrips there and enable Beijing to draw a “strategic triangle” linking reefs and islands in the Paracel Islands to the west and the Spratlys to the south, effectively fencing off the South China Sea, experts say. That could pave the way for Beijing to declare a possible air defense identification zone in the area, demanding commercial and military aircraft seek permission before flying through it.

Allowing China to seize complete control of the shoal and launch land reclamation work would represent a “geopolitical loss” for Washington that would be unacceptable, Blair said.

For the United States, the Scarborough Shoal represents “at least a pink line, if not a red line,” Blair said.

If a clash erupted, China would find itself in a difficult position, hundreds of miles from its military bases. Any Chinese aircraft would need to be refueled just to arrive at the location.

“From everything I know militarily, that would be a bad place for China to pick a fight,” he said.

The feud over Scarborough Shoal flared up in 2012, and the United States tried to mediate a deal to defuse the argument. The Philippines complied with the deal and withdrew its ships, but the Chinese never pulled back their vessels and continue to deploy ships at the mouth of the shoal’s bay.

The United States has conveyed its solidarity with the Philippines through a number of symbolic steps in recent months, but has stopped short of publicly announcing any red lines.

Asked if the United States had issued a warning to China not to undertake land reclamation at Scarborough Shoal, State Department spokesperson Anna Richey-Allen said the United States regularly holds discussions with Chinese officials about developments in the South China Sea.

“Since 2012, Chinese Coast Guard vessels have sought to block fishing access to the area, restricting the long-standing commercial practices of others. We are concerned that such actions exacerbate tensions in the region and are counterproductive,” she added.

In April, U.S. Defense Secretary Ash Carter made a point of stepping foot on an American aircraft carrier, the USS John C. Stennis, as it patrolled waters west of the Philippines. He then paid a visit to the annual Balikatan exercise, which involved 5,000 troops from the United States, 3,500 troops from the Philippines, and 80 forces from Australia and included an amphibious operation on a hypothetical South China Sea island.

After the exercise, the Pentagon sent out A-10 Thunderbolt warplanes to conduct patrols over Scarborough Shoal.

The United States also has announced plans to rotate troops and aircraft at five bases across the Philippines under a new military cooperation agreement, marking a dramatic about-face in relations as Manila kicked out all American forces more than two decades ago.

Before the ruling from the international court on Manila’s complaint, China has been lobbying other countries for support and launched a public relations campaign to make its case. It apparently scored a diplomatic victory this week when Southeast Asian countries backed off a statement critical of Beijing over its policies in the South China Sea.

The original statement issued Tuesday from foreign ministers from the Association of Southeast Asian Nations underlined the importance of freedom of navigation in the waterway and expressed concern over developments that had “eroded trust and confidence.” But Malaysia’s foreign ministry later retracted the statement without offering an explanation.